UCN𝜏 Energy Spectrum Sensitivity Studies

In the UCN𝜏 neutron lifetime experiment ultracold neutrons (UCN) are generated in a superthermal deuterium source, stored in a vessel called the roundhouse, where their energy spectrum is allowed to equilibrate, and finally trapped in a magneto gravitational trap, where their lifetime is measured. During a run cycle it is essential to understand the changes in the equilibrium energy spectrum which gets loaded into the magneto gravitational trap volume. Changes in the spectrum can occur due to source hardening in the deuterium, where deuterium ice forms, changing the crystal structure and trapping low energy UCN; these changes can be detected using energy spectrometers in the roundhouse.

Here multiple spectrometers are simulated to determine the ability for each different method to reproduce the UCN energy spectrum in the roundhouse and therefore the trap. The spectrometry methods used were a time-of-flight chopping wheel spectrometer, a gravitational potential “Elephant Trunk” spectrometer, a height dependent scintillating UCN detector, and a draining dump detector. Each instrument used multiple changing spectra loaded into the roundhouse to determine both their sensitivity to source conditions and their ability to reproduce the correct equilibrium energy spectrum. I will compare the simulated spectra and discuss how these spectrometers can be used to gain a clear picture of the energy spectrum as it changes during a run cycle of the UCN𝜏 experiment.